Polyolefin compositions



United States Patent 3,248,359 PQLYQLEFlN CQMPQSHTHQNS Daniel EdwinMaloney, Wilmington, Del, assignor to E. I. du Pont de Nemours andCompany, Wilmington, Del, a corporation of Delaware No Drawing. FiledApr. 27, 1961, Ser. No. 105,857 8 Claims. (Cl. 260-411) This applicationis a continuation-in-part of Serial No. 1,847, filed January 12, 1960.

The present invention relates to polyolefin compositions, and, moreparticularly, to modified polyolefin com-- positions having improvedproces-satbility and improved stress-crack resistance.

The present invention is directed to the high molecular weight resinsobtained by the polymerization of terminally unsaturated monoolefins.Representative example-s of such polyolefins are low and high densitypolyethylene, polypropylene and copolymers of ethylene with suchmonomers as propylene, butene, octene, decene and vinyl cyclohexene.These polyolefins are generally obtained either through polymerizationwith a free radical catalyst, or through polymerization with anorganometallic catalyst, often referred to as a coordination catalyst.The molecular weights of high molecular weight polyolefins range fromabout 2000 to about 40,000 and higher. These polyolefins, furthermore,are characterized by inherent flexibility, corrosion resistance,weatherability, and outstanding dielectric properties; and, because ofthese properties, the polyolefins are particularly valuable in numerouscommercial applications. In many applications the polyolefins areemployed in stressed conditions. This is particularly true in the use ofpolyolefins for wire and cable coating and jacketing. In this stressedcondition, polyolefins fail significantly more readily than in theunstressed conditions. This is particularly true when the stressedpolyolefin is contacted with surfaceactive agents which include soaps,detergents, alcohols, polyglycol ethers, silicones and various otheraliphatic and aromatic hydrocarbons. In general, this phenomenon isreferred to as environmental stress-cracking and has been a real problemin the commercial development of polyolefins.

It is, therefore, one of the objects of the present invention to provideimproved polyolefin compositions. It is another object of the presentinvention to provide polyolefin compositions which are improved in theirenvironmental stress-crack resistance. Another object of the presentinvention is to improve the processability of polyolefins. Other objectswill become apparent hereinafter.

The objects of the present invention are accomplished by a homogeneouslyblended polyolefin composition comprising a polyolefin containing from 1to 50% by weight of said polyolefin, and preferably from 1 to 15% byWeight of said polyolefin, of an ethlylene copolyrner wherein thecomonomer is a compound capable of copolymerizing with the ethylene andforms a copolymer having polar groups directly attached to the polymerchain, the ratio of the ethylene to said .comonomer in the copolymervarying from 1:1 to 30:1, the molecular weight of the copolymer beingsufliciently high .to give the copolymer a melting point above 70 C.

Comonomers which results in copolymers having polar groups attached tothe carbon chain of the molecule are such compounds as carbon monoxide,vinyl acetate, vinyl alcohol, vinyl ethers, unsaturated acids andsimilar compounds. A preferred class of comonomers are those whichcontain oxygen in the polar group and which contain not more than twocarbon atoms in the polar group attached to the polymer chain. Thepreparation of these Patented Apr. 26, 1966 ICC copolymers, having thedesired ratio of comonomers and the desired molecular weight, is wellknown in the art, and, therefore, not described in great detail here. Ingeneral, these copolymers are formed by the copolymerization of ethyleneand a suitable polar group containing comonomer at elevated temperaturesusing a free radical catalyst, such as a peroxide, in the presence orabsence of an aqueous phase. Certain copolymers employed in the processof the present invention require an additional processing step afterpolymerization, such as the preparation of copolymers of ethylene andvinyl alco hol, which are only obtained on hydrolysis of ethylene/ vinylacetate copolymers.

The polyolefins stabilized by the process of the present invention areobtained through the polymerization of an olefin having the generalformula CH =CHR, where R may be a hydrogen or a hydrocarbon radical. Thehydrocarbon radical may be aliphatic, cycloaliphatic or aromatic innature. They are high molecular weight polymers suitable as plasticswhich generally have molecular weights, as determined by melt index,ranging from 0.01 to 35. Employing the recently developed coordinationcatalyst, there appears to be little or no limitation on-the size of thehydrocarbon radical in the monomer in obtaining high molecular weightpolymer. However, from a commercial standpoint, the polyolefins aregenerally limited to monomers containing less than 20 carbon atoms. Thepolyolefin class includes copolymers of these olefins with one or moreother monomers. These copolymers may be made in any range of comonomerconcentration. Although the improvement discovered in accordance withthe present invention is applicable to all polyolefins, it isparticularly significant with such polymers as polyethylenes,polypropylene, and copolymers of ethylene with terminally unsaturatedolefins containing more than 50% of ethylene.

The polyolefin compositions employed in the present invention may alsoinclude, in addition to the above modifiers, other additives which areemployed to plasticize, lubricate, prevent oxidation or lend color tothe polyolefin. Such additives are known and may be incorporated withoutappreciably affecting the advantageous results obtained by the presentinvention.

The resistance to environmental stress cracking is measured by .atechnique described in the book Polyethylene by Raff and Allison,published by Interscience Publishers, on pages 389 to 393. Principally,the method comprises cutting a slit into ten specimens and bending thesespecimens into a U-shape with the slit on the outside, and, while sostressed, placing the specimens into a surface-active agent. Thesurface-active agent employed generally is Igepal CA, an alkyl arylpolyethylene glycol ether manufactured by General Dyestuff Corporation.The measurement which determines the resistance to stresscrack-ing isthe time required for 50% of the stressed samples to fail. In manyinstances it was found that Igepal CA did not produce cracking of thestressed samples rapidly enough to allow significant measurements.Hence, the measurement of environmental stress-crack resistance was alsocarried out in Hostapal using the same procedure. Hostapal, similarly,is a detergent comprising an ethylene glycol phenol condensationproduct, and is also commercially available. A more severe test was alsoformulated by exposing the stressed samples to a temperature of 70 C. inan air oven for 7 days, and thereafter submerging the stressed sample ina detergent such as Igepal AC or Hostapal. Improvement in processabilityis measured by various methods. One method comprises the measurement ofthe stress exponent n and the measurement of the processability index C.An increase in either It or C measures an improvement in How of thepolyolefin. The stress exponent n is defined as the resultant mixturethrough a two inch Egan extruder at a temperature of 170 to 220 C.,using either a typical nylon extrusion screw or a mixing torpedo in theextruder.

n =log In each instance where the tables show an unmodified poly- 5olefin for comparative purposes, the data listed was obwhere 7 is theshear rate at 2160 g. loading of a melt tained from a polyolefin whichhad been worked in the indexer, 7 is the shear rate at 6480 g. loadingof the same Way as the modified polyolefins. melt indexer, 0' is theshear stress at 2160 g. loading of Compositions prepared in this mannerwere tested in rethe melt indexer, and a is the shear stress at 6480 g.spect to their environmental stress crack-resistance using loading ofthe melt indexer. The processability index is 10 the more severe testmethod described above, involving defined as I heat aging of thesamples. Table I describes the results 10 obtained from variouspolyolefins employing as an addi- C =M I X tive an ethylene carbonmonoxide copolymer in various concentrations. The carbon monoxidecopolymer em- Where n is the stress exponent and MI the melt index.ployed had a melt index of approximately 500 to 1000" The measurement ofmelt index and the indexer used dg/min, andarnelting point ofapproximately 97 C. As herein are described in d tail in A D1 852 can beseen from the results, a significant improvement in The improvement inprocessability is also manifested by environmental-stress crackresistance results when the a lowering of head P afld Power q m nts inethylene/ carbon monoxide copolymer is employed as an melt extruders,such as are used in applying insulation to additive in eitherpolyethylene or copolymers of ethylene wire and cable. Another method ofmeasuring the imwith monoolefins.

Table I Melt index Density Environmental stress crack resist- I Percent13/00 in (lg/min. in g./ec. anee after 7 days aging, in hours PolymerE/CO ratio (ASIM-D- ASTM- copolymer 1238-52-1) D792 In Igepal CA InHostapal Polyethylene- 0. 1. 75

Do 5 3.5 0. 30 3 Do 10 3.5 0. 21 0 Do 5 3.8 0.15 30 Polyethylene and 0.23 O. 75

polyethylene wax. Ethylene/butene copolymer 97:3 1. 87 0.937 D0. 5 3. 52. as 0. 941 00 provement in processability is to measure the maximumex- The improvement in processability is demonstrated by trusion speedpermissible for acceptable wire coatings or the results listed in TableII. Compositions were prepared to measure the surface roughness of theextruded wire from two branched polyethylenes, A and B, having a made ata particular speed. density of 0.92 g./cc. with varying concentrationsof the Various methods may be employed to obtain the comethylene/carbonmonoxide copolymer, and with' copolypositions of the present invention.Thus, the novel polymers varying in their comonomer ratio. Thecopolymers olefins of the present invention may be prepared by millingemployed had substantially the characteristics of those a physicalmixture of the two components on a rubber mill used in obtaining theresults in Table I. The stress exat temperatures above the melting pointof the polyolefin, ponent n and the processability index C were measbybanburying a mixture of the two components, by disured and calculated asdescribed hereinabove. These solving both in a common solvent and thenprecipitating polymers were then employed to coat number 22 gauge andseparating the mixture, and by melt extruding a dry wire at 600ft./rnin. employing a 1% inch N.R.M. exblended mixture of the polyolefinand the additive. The truder using a conventional pressure type die. Thepolymethods used in incorporating additives into polyolefins mer meltwhen emerging from the die was at a temperature have been described inthe art, and, since they are not of 220 to 225 C. Both barrel and diewere maintained critical, are here not disclosed in any substantialdetail. at a temperature of approximately 245 C. The pres- The presentinvention is further illustrated by the exsure at the exit end of thebarrel and the power necessary perimental data described and listed inthe tables below. to rotate the screw of the barrel were measured. TheThe novel compositions illustrated in these tables were results listedindicate the substantial improvement in generally prepared by dryingtumbling finely divided polyprocessability resulting from the additionof the ethylene/ olefin and finely divided copolymer additive andextruding carbon monoxide copolymer.

Table II Percent Melt Stress Process- Head Power, Polymer E/CO E/COindex exponent ability pressure, in watts copolymer ratio in dg./ 77index C in min. p.s.i.g

Substitution of the ethylene carbon monoxide and ethylene vinyl acetatecopolymer by an ethylene/vinyl methyl ether copolymer containing 20% ofvinyl methyl ether, .an ethylene dimethyl fumarate-copolymer containing18% of dimethyl fumarate, an ethylene vinyl alcohol copolymer containing35% of vinyl alcohol, and a copolymer of ethylene and methyl acrylatecontaining of methyl acrylate shows the same type of improvements instress crack-resistance and processability as shown in the precedingtables.

In Table V a comparison of stillness and, stress crack Table Iresistance is given for a blend of high density polyethylene, a densityof 0.96 g-./cc. and a melt index of 0.8 dg./ Percent Melt R0ugh min.with an ethylene/vinyl acetate copolymer having an Polymer E/CO E/ooindex nessin 15 ethylene to vinyl acetate mole ratio of 21, a melt indexcopolymer who Q E 3 38 of 0.8 dg./min. and a melting point of about 110C., and

' two commercially available high density polyethylenes. Ethylene/butenecopolymer, 97:3 0 1.83 152 o 10 -4 2. 33 57 Polypropylene 0 0. 33 32 o 5-4 0.40 17 Table V Stress Resin Density, Melt Stilfncss 2 crack g./cc.index 1 psi. resistance F50 hours 3 2 ASIM-D-747-58T 3 AS'IM-D-IGQBmodified in that the test was carried out in annealing the samples forone hour.

The improvement in stress crack resistance and processability obtainedby the addition of an ethylene/vinyl acetate copolymer to polyethyleneis demonstrated by Table IV showing percentage of ethylene/vinyl acetatecopolymer added, the melt index of the resulting polymer blend, the headpressure observed in the extrusion coating of wire, and the stress crackresistance as measured on samples of the blend which had been exposed to70 C. temperature in air for seven days in Hostapal. The ethylene/ vinylacetate copolymer employed in the formation of the blend giving rise tothe data presented in Table IV was a copolymer having a melt index ofabout 1.8 dg./min., a melting point of about 110 C. and con- Joydetergent without As can be seen from the data, the stresscrack-resistance of the blend is greatly improved over that obtained forthe unmodified polyethylene. Additionally the blend also gives the bestcombination of stress crack-resistance and stifiness.

In Table VI a comparison of stiffness and stress crack resistance isgiven for blends of low density polyethylene and an ethylene methacrylicacid copolymer having an ethylene to methacrylic acid mole ratio of 16,a melt index of 150 dg./min. and also a blend of the same polyethylenewith an ethylene vinyl acetate copolymer having an ethylene to vinylacetate ratio of 7 and a melt index of 12.

ASTM-D-1238-57'1. 2 ASTMD-l693 modified in that Hostapal was usedinstead of Igepal.

tained 15% of vinyl acetate. The test procedures employed were the sameas employed in the determination of the data listed in the precedingtables.

The experimental results illustrated in the tables are characteristic ofthe nature of the improvement obtained by the compositions of thepresent invention. Polyolefin compositions prepared from suchpolyolefins as polybu tene, and other copolymers of ethylene andmonoolefin, have been found to exhibit substantially the sameimprovement in stress crack resistance and processability when combinedwith copolymer additives of the type described above, in theconcentrations described above. Similarly, the specific nature of thepolar group does not affect the ability of the copolymer to improve thestress crack resistance and processability of the polyolefin. Theinvention is, therefore, not to be construed as being limited to theexperimental data presented in the tables.

The compositions prepared by the process of the present invention areuseful in the molding of solid shapes, in the extrusion of film, fibers,tubing and pipe, but are of particular utility in the coating of wiresand cables. Standard polyolefin fabrication methods can be suitablyemployed with the compositions of the present invention.

I claim:

1. A composition of matter comprising a homogeneous blend of apolyolefin and from 1 to 15% by weight of the polyolefin, of a solidcopolymer of ethylene and carbon monoxide, wherein the ratio of ethyleneto carbon monoxide varies from 1:1 to 30:1.

2. The composition of matter set forth in claim 1 4 wherein thepolyolefin is polyethylene.

3. The composition set forth in claim 1 wherein the polyolefin is acopolymer of ethylene and a comonomer having the general formula RCH =CHwherein R is an aliphatic hydrocarbon radical.

4. The composition set forth in claim 1 wherein the polyolefin ispolypropylene.

5. The composition as set forth in claim 1 containing a carbon blackadditive.

6. The composition set forth in claim 1 containing an antioxidantadditive.

7. The composition set forth in claim 1 in film form.

8. The composition set forth in claim 1 in funicular form.

References Cited by the Examiner UNITED STATES PATENTS 2,448,666 9/1948P16161161 260897 2,541,987 2/1951 Cr-arner 260-897 2,628,214 2/1953Pinkey et al 26041 2,953,541 9/1960 Pecha 26033.4

' FOREIGN PATENTS 582,093 11/1946 Great Britain.

MURMY TILLMAN, Primary Examiner. v

20 LEON J. BERCOVITZ, Examiner.

1. A COMPOSITION OF MATTER COMPRISING A HOMOGENEOUS BLEND OF POLYOLEFIN AND FROM 1 TO 15% BY WEIGHT OF THE POLYOLEFIN, OF A SOLID COPOLYMER OF ETHYLENE AND CARBON MONOXIDE, WHEREIN THE RATIO OF ETHYLENE TO CARBON MONOXIDE VARIES FROM 1:1 TO 30:1. 